Generally, certain heavy construction machines are used to fulfill various functions by means of reconfiguring the work equipment. In fact, a traditional work machine, which has one or more arms, could have an attachment for a particular function fixed to its arm. Therefore, a bucket is generally used as a loader as it allows the loading of earth or other material to be transported and unloaded at another destination.
A loader is specifically used during leveling operations. In this case, the movement of the arm in relation to the chassis is left floating so that the bucket can move by scraping the ground and by evenly piling the mound of earth on which it rests. To free up the position of the bucket, usually the two piston chambers that control the direction are engaged. Thus, the machine works on what is known as a “floating” mode of command.
In practice, this “floating” command is obtained by reconfiguration of the hydraulic circuit achieved by the movement of manipulator controls in a particular position. Therefore, in a classic manner, the manipulator has a mobile inclined lever that will deliver variable pressure control based on this inclination. The “floating” position is normally found at the end of the manipulator stroke, which allows the generation of excess pressure in the control circuit. This excess pressure leads to the movement of the slide valves of the main distributor in such a way that the two piston chambers that are engaged become connected.
Furthermore, this same type of machine could also be used for lifting work. In that case, the tool that is attached to the working arm extremity is adapted for this kind of work and, for example, could be a pallet forklift or any other lifting mechanism. Then the hydraulic circuit of the piston chambers is generally equipped with valves known as “safety valves,” used to insulate the piston chamber undergoing consecutive pressure from the weight of the load lifted.
In fact, in case there is a rupture in the piping of the hydraulic circuit it is important to be able to prevent this chamber from emptying too rapidly, which would cause the load to fall.
A safety problem could arise for machines which work in both loading and lifting modes. In fact, when it is in lifting mode, if an operator inadvertently moves the manipulator into the position known as the floating position while the two piston chambers are connected, the load will fall on the ground. This situation is unacceptable for obvious safety reasons.
For this reason, it was proposed that the floating control position for machines that work as both loaders and lifters should be eliminated.
At the same time, we think that this radical solution limits the performance of the machines mainly in leveling operations.
One of the objectives of the invention is to be able to combine the possibility of a floating position for use in loading with a high level of safety.